Numerous monophosphate derivatives are known to be effective fire-retarding agents. In general, however, polyphosphoric acid derivatives have not been used as fire-retarding agents. In particular partial esters of polyphosphoric acid have not been suitable because of the presence of residual acid functionality which is likely to adversely affect cellulosic materials with which it is brought into contact.
Furthermore, monophosphate derivative fire-retarding agents are generally regarded as nonpermanent. Such fire-retarding agents are susceptible to leaching from the cellulosic material upon contact with water. Cellulosic materials so exposed are thereby rendered less resistant to fire. In U.S. Pat. No. 3,565,679 a list of non-permanent fire retardants includes the phosphates.